1. Field of the Invention
The present invention relates to an image forming apparatus which can automatically measure a width of a recording medium such as paper, facilitate determination of an image formation width, improve image transfer quality and further improve a control characteristic of an image formation start position.
2. Description of the Related Art
In an image forming apparatus, such as a printer, for forming an image including characters on a recording medium such as paper, an image formation width, such as a print width, is determined depending on a width of paper. Therefore, an operator uses a given setting means to set the paper width in advance so as to indirectly set the print width.
There is available such an image forming apparatus, wherein for automatically setting a paper width, sensors are disposed in a paper width direction near a paper feed means for detecting the paper width. However, printing is carried out with a given print width regardless of the detected paper width.
With the foregoing arrangement, no problem may be raised when an image is formed on only one side of the paper. This is because, in this case, a print start position (image formation start position) is unchanged even if a paper width is changed (the paper width is used only for determining a print end position).
On the other hand, in case of forming images on both sides of the paper, a change of the paper width cannot be dealt with. This is because a print start position is changed on the reverse of the paper depending on the paper width.
Further, in an image forming apparatus wherein toner is adhered to a charged drum and the paper is pressed thereupon to carry out image transfer, charging is caused from an end of the paper (in case of continuous paper, also via paper feed holes of the paper formed near the end thereof) to deteriorate the transfer quality (print quality). This is significant particularly in such an image forming apparatus wherein the paper width is changed.
Further, when high-priced photosensors are used as the foregoing sensors, the sensors are minimized in number and disposed only at positions corresponding to paper widths to be used. Thus, if a paper width which is not expected is used, the paper width cannot be detected.